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Brill, R. H. "Chemical studies of Islamic luster glass." Scientific methods in medieval archaeology, chapter XVI. Berkeley, CA: U of Calif. P, 1970. pp. 351-377. UCLA CENTER FOR MEDIEVAL AND RENAISSANCE STUDIES CONTRIBUTIONS: IV Scientific Methods in Medieval Archaeology Edited by RAINER BERGER Z CHAPTER OFFPRINT _ ~NIYERSITY OF CALIFORNIA PRESS BERKELEY, LOS ANGELES, LONDON, 1970 NK 51,08 .5 .B85 ••••• Rakow Research Library, The Corning Museum of Glass - http://www.cmog.org Brill, R. H. "Chemical studies of Islamic luster glass." Scientific methods in medieval archaeology, chapter XVI. Berkeley, CA: U of Calif. P, 1970. pp. 351-377. XVI CHEMICAL STUDIES OF ISLAMIC LUSTER GLASS R. H. Brill fJUSTER DECORATIONS are thin metallic films applied to ~ the surfaces of ceramic objects. Since its beginnings, possibly as early as the fourth century A.D., but certainly by the ninth century, the technique of film application has seen frequent use down to the present day. In different times and at different places it has been used to produce a wide variety of colors and appearances, ranging from highly reflecting mirrorlike surfaces to faintly perceptible iridescences. Numerous kinds of colored stains and glazes have often accompanied luster effects and in some cases have so enhanced the ornamentation that these stains and glazes themselves have come to be termed "lusters" even though metallic films may not be present. Because lusterwares vary so much in style and are broadly distributed geographically-and even more so because of the somewhat complicated technologies involved in making them-there must be many cases where analysis and examination of ancient fragments would be of use to those concerned with medieval studies. The historical spread of the technique has been much discussed by art historians, and both the technology and matters of stylistic identification are usually treated as being well under­ stood. Such may very well be the case. Laboratory studies of sufficiently large numbers of representative wares, however, would undoubtedly prove very worthwhile either for verifying the existing theories or for answering questions about problematical pieces. Analysis of the luster glazes themselves and analysis, X-ray diffraction, and petrographic ex­ amination of the fabrics would all probably be helpful,l 1 In preparing for this study, a literature search , indicated that few, if any, analyses had been made of luster decoration on glass and only a few of pottery of Islamic origin. However, realizing that analyses or studies of this sort might well have been published in places familiar only to Islamic scholars, the accompanying bibliography should not be relied upon as being complete. One analytical study 35 1 Rakow Research Library, The Corning Museum of Glass - http://www.cmog.org 33755 Brill, R. H. "Chemical studies of Islamic luster glass." Scientific methods in medieval archaeology, chapter XVI. Berkeley, CA: U of Calif. P, 1970. pp. 351-377. 352 ISLAMIC LUSTER GLASSES The scope of the present paper, however, is not intended to be so all­ encompassing. The work described here has been confined to one very limited aspect of luster decoration. The main objective has been to see what could be learned about one specific group of luster glass fragments. There are four significant lines of glass research which converge on the group of fragments studied here. In the first place, the glasses were most likely made in the Islamic glass factories at Fustat, near present-day Cairo. Therefore, the analysis of the glasses themselves should be fitted into the systematic cataloging of compositions of ancient glasses that are being developed.2 Future analysis of groups of luster glasses (and their glazes) from different parts of the Islamic world might well show com­ positional differences that could be helpful in characterizing the wares made at different factories. Even a casual examination of the most common type of luster decora­ tion on Islamic glass, a deep transparent amber stain, suggests that it is a silver stain. Thus Islamic luster glass can be considered to form a histori­ cal link connecting the earliest known use of silver and/or gold in ancient glass, for coloring a small group of Late Roman dichroic glasses,3 with the use of silver for making the yellow-stained glasses of the cathedral windows of Western Europe. The chemical formulation of the Islamic luster glazes also is of some interest from the viewpoint of the history of chemistry, for there is at least one extant recipe for luster glazes for pottery in the early Persian appears in an appendix to F. Sarre, Die Ausgrabungen von Samarra, Band II (Berlin), pp. 95-100. Also a series of early papers were presented by L. Franchet, who concerned himself with the technology of Islamic luster glazes. See, for example, Comptes Rendus, vol. 141 (1905), 1020-1022, 1237-1240; Ann. Chim. Phys. (8), 9 (1906 ), 37, 227; Trans. Brit. Ceramic Soc., vol. 7 (1907), 7I. 2 The most noteworthy of these is that being compiled by E. V. Sayre and R. W. Smith. See, for example, E. V. Sayre and R. W. Smith "Compositional Categories of Ancient Glass," Science, vol. 133 (9 June 1961), 1824-1826, and "Some Ancient Glass Specimens with Compositions of Particular Archaeological Significance," (BNL-879 T-354) Brookhaven National Laboratories (July 1964). Other large, bodies of analytical data are being compiled by M. A. Besborodov in Leningrad and by the author at The Corning Museum of Glass. Analyses up to 1957 have been tabulated and reinterpreted by Earle R. Caley in his Analyses of Ancient Glasses, 1790-1957 (New York: The Corning Museum of Glass, 1962). 3 R. H. Brill, "The Chemistry of the Lycurgus Cup," paper no. 223, Comptes Rendus, II, VIIth International Congress on Glass, Brussels, 1965, International Commission on Glass. Rakow Research Library, The Corning Museum of Glass - http://www.cmog.org Brill, R. H. "Chemical studies of Islamic luster glass." Scientific methods in medieval archaeology, chapter XVI. Berkeley, CA: U of Calif. P, 1970. pp. 351-377. ISLAMIC LUSTER GLASSES 353 literature, and others are known from Hispano-Moresque and Italian sources. The fourth line of research is of a fundamental chemical nature, and deals with the broad question of the nature of the colorants used in ancient red, orange, and yellow opaque glasses. Two of the types of luster studied here are red opaque and yellow opaque stains. In the sections that follow we shall review the history of luster decora­ tion, describe the samples studied, record the results of several types of experiments, and interpret the experimental results in terms of the lines of research indicated above. It must be added that these results can only be considered provisional, because experimental work is still in process as this paper is being prepared. The History of Luster Decoration Although the topic has been much discussed, leading authorities do not agree upon either the place or date of the origin of luster decoration. Indeed the discussion has at times become so lively that one not well versed in all the arguments hesitates to comment even casually upon the question. The most favored authoritative dates range from the eighth­ ninth century back to as early as the fourth-fifth century A.D., and the favored places of origin seem to be Egypt, Persia; and Mesopotamia.4 Although questions of origin are sometimes finally relegated to unim­ portance, it does seem that in this case the question could ultimately be of considerable importance in the history of glass-even if not so in ceramics. The question is sharpened by the viewpoint of Lamm that the technique of luster decoration originated with the "glass painters of Egypt." It would be of value to determine the place and date of origin of such a readily recognizable decoration, because this could perhaps be of help in 4 From the many possible references, we single out here a few containing general discussions of lusterwares. R. Ettinghausen, "An Early Islamic Glass Making Center," Record of the Museum of Historic Art, Princeton University, vol. 1 (1942), 4-7; A. W. Frothingham, Lustreware of Spain, Hispanic Society of America, New York (1951); C. J. Lamm, Oriental Glass of Medieval Date Found in Sweden and the Early History of Lustre-Painting (Stockholm, 1941). See esp. pp. 18-33; A. Lane, Early Islamic Pottery (London: Faber and Faber, 1947), pp. 14-20 passim; A. V. Pope and P. Ackerman, A Survey of Persian Art>, vol. II (Oxford University Press, 1939), pp. 1469, 1487-1498, 1545-1558, and esp. 1701-1702; Hans E. Wulff, The Traditional Arts and Crafts of Persia (M.LT. Press, 1966). Rakow Research Library, The Corning Museum of Glass - http://www.cmog.org Brill, R. H. "Chemical studies of Islamic luster glass." Scientific methods in medieval archaeology, chapter XVI. Berkeley, CA: U of Calif. P, 1970. pp. 351-377. 354 ISLAMIC LUSTER GLASSES telling us to just what extent glass craftsmen did move around in ancient times, and more importantly it might help to clarify our pictures of the ways in which the ancient and indigenous glass industries of the Near East developed into those of the Islamic Period. We might observe here that the recent discovery at Fustat of the earliest known dated piece of luster glass, a beaker bearing the date of 771--772,5 lends some support to the view that the technique originated with the glass painters of Egypt. There were several well-known centers producing luster-decorated pottery, and possibly glass, during the Islamic Period. Some of these were Baghdad and Basra in Iraq, Kashan in Persia, and Fustat in Egypt. The art spread westward via North Africa, and inspired the famous Hispano­ Moresque ceramics which reached an artistic peak in the fifteenth century, and to Majorca and Italy where it was incorporated into majolica ware.

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